In the making of commercial microwave link components there is a constant struggle with cost and quality issues in order to fulfill customer demand and cope with market competition.
Usually a diplexer is a purchased pre-tuned part with a fixed sub-band. This means that different diplexers are required depending on what sub-band the user wants.
A common design approach of a microwave link outdoor unit is to stack the PCB, the shielding cover, the diplexer, and the waveguide nose. Since all parts have mechanical tolerances, it is a problem to solve the sum of the mismatch of these different components in order to get a weather proof unit.
This solution of assembly design will only let the PCB come in close contact with one side of the cabinet. The thermal distance to the other side is much longer due to shielding cover diplexer and waveguide nose. This leads to a problem with heat sink performance and hence increased internal temperature in the outdoor unit.